The invention relates to a composition having high thermal stability and good sealability properties. More particularly, the invention relates to improved gasket materials.
Gaskets and other seals are required for use in many applications where adjacent surfaces are to be sealed to prevent fluid or gas leakage. One application where gaskets are particularly important are as head gaskets for automobile engines.
A variety of materials are used in gasket manufacture. Among the different types of gasket materials are composite gasket materials made by a wet laid process (often known as Beater Addition gasket material), expanded graphite gasket materials, and multilayer steel gasket materials.
Expanded graphite gasket materials are comprised of expanded graphite flake which may contain a small amount (1.0% or less) of a polymeric resin such as phenolic resin or polyvinyl alcohol, serving as binder material. These gasket materials can be rather expensive and are effective at relatively high operating temperatures, up to about 550.degree. C. However, one disadvantage of these materials is their low resistance to compressive forces, especially after exposure to fluids such as oil or antifreeze.
Multilayer steel gasket materials are made of multiple layers steel, both flat and embossed, and may include a coating such as fluorine, silicone, epoxy, or nitrile butadiene rubber. These gasket materials are intended for harsh environments and may be used at operating temperatures above about 550.degree. C. A drawback of such materials is that they require excessively smooth and expensive joint surfaces.
Composite gasket materials made by a wet laid process (Beater Addition gasket materials) are comprised of a fiber component which is distributed within an elastomeric binder matrix, together with property improving solid fillers. These materials may be modified by silicone saturation to improve their thermal and sealability properties. Moreover, these materials may be used alone as "soft" gasket materials for some applications, or they may be laminated to steel, forming "hard" gasket materials for other applications. The maximum operating temperature at which these gasket materials normally may be used is between about 200.degree. C. and 250.degree. C.
Some gasket applications, particularly for use as automobile head gaskets, use Beater Addition gasket material. This type of gasket, as noted above, includes a fiber component and a filler dispersed in an elastomeric binder matrix. The fiber can include various synthetic or mineral fibers which help to improve processability of the material. The binder is generally a polymeric elastomer which provides a matrix to secure the other components which form the gasket. The filler includes solid materials such as kaolins, mica, graphites, diatomaceous earths and other such materials, which impart desirable mechanical properties to the composite material.
Beater Addition gasket materials are often used in harsh environments where they are subject to chemical solvents, to temperatures which often exceed 200.degree. C., and to high pressures. As a result, the properties which these materials must exhibit include crush resistance, chemical resistance, thermal stability and suitable sealing properties. To some extent, the properties can be varied by adjusting the ratios of fiber, binder and filler. Typically, an increase in the amount of the binder component improves sealability, but usually at the expense of the heat stability. Similarly, a decrease in the binder content compromises the sealability while improving the heat stability. While the alternative gasket materials, such as expanded graphite and multilayered steel, tend to provide good thermal stability as well as good sealing properties, the cost of these materials is extremely high and may be prohibitively high for some applications. Moreover, both the expanded graphite and multilayered steel gasket materials have their associated drawbacks mentioned above.
There is thus a need for a Beater Addition gasket material which has improved thermal stability and sealing properties.
Accordingly, it is an object of the invention to provide a Beater Addition gasket material which combines high thermal stability with good sealability properties and good chemical resistance. It is also an object to provide such a gasket material which retains high resistance to compression forces after exposure to fluids and which is able to seal joints having somewhat rough flange surfaces. Another object of the invention is to provide an economical gasket material with superior properties. A further object of the invention is to provide a gasket material suitable for use as an automobile head gasket. Other objects will be apparent to those having ordinary skill in the art upon reading the invention disclosure which follows.